


Double Trouble

by NihilismPastry



Series: Requests from Tumblr [19]
Category: Undertale (Video Game)
Genre: Cunnilingus, Double Penetration, F/M, Multi, Rough Sex, Soul Mate AU, Threesome, Yandere Blueberry, Yandere Swapfell Sans, ecto tongue, ectodick
Language: English
Status: Completed
Published: 2016-12-15
Updated: 2016-12-15
Packaged: 2018-09-03 00:39:13
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,493
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8689819
Author URL: https://archiveofourown.org/users/NihilismPastry/pseuds/NihilismPastry
Summary: You had ended up in a homicidal world known as the Underground, and had quickly gotten used to the people there, even bonding with the captain of the royal guard, Sans. However,after an accident, you both are transported to an eerily familiar world, just less homicidal. Oh, and Sans exists in this world too, and also wants to fuck your brains out.





	

**Author's Note:**

> A request from an Anon over at Tumblr. 
> 
> Anon: Can you make SwapFell!Sans x Reader x Swap(Sans)? Both skeleton could get jealous of each other with the reader, so they could fight and compete against each other, until the reader decides to fuck them both? With reader in middle? I love yours stories.

You had always been one to do your best. People may have called you an over achiever,  it you liked to throw yourself into a project. That was why you passed high school with flying colors, braved through many a narcissistic college professor, and had survived living in a world hell bent on killing you. The ability to work hard and stay optimistic had saved you countless times over. That passion had even gained the attention of the captain of the Royal Gaurd, and he had proceeded to marry you. Well, the monster equivalent of it anyway. 

You were happy enough with the marriage, Sans was strange to be sure, but he treated you well enough. His brother didn't accept you by any stretch of the imagination, but from what you could tell,he didn't approve of anyone getting close to his brother. All in all you were happy with the arrangement. You had no doubt drive to leave for the barrier, the world you left behind so boring and mundane compared to the Underground. Then again, you became a bit of an adrenaline junkie since you entered this world. While Sans often complained about it being boring, you found yourself dodging magic and weaponry on a daily basis.    

However, your life went from exciting to downright strange over the course of a single night. Undyne had come over to work on something with Papyrus, just for the thing to set the house on fire. Instead of being burnt alive, you and Sans found yourself in a world that was similar to your own. Instead of everyone trying to kill you though, most people were friendly...In fact the new version of Sans, who you called Blueberry, invited you to live with him and his brother.  

You sighed as you sat up on the couch, sleep still evading you even if it was three in the morning. Going over memories was a way for you to fall asleep in college, but the tried and true trick wasn't working. You glanced down to the heavy weight on your stomach, Sans had his arms locked around your waist, his head burried in your stomach, and your hands were tied together with his scarf, a ritual since he had started showing interest in you. You ran a hand along his skull, humming when he snuggled closer to you.  

You looked up when you heard a door open and shut, and heavy footfalls along the stairs. You were unsurprised to find Blueberry walking down the stairs. The small skeleton never seemed to sleep, and if he did it was for a few hours. His eyes lit up when he spotted you, and he made his way over, a book in his hands. HI, SWEETHEART." 

You wrinkled your nose at the nick name. Blueberry had a crush on you, and made no attempts to hide it. You had tried to get him to stop, especially when Sans got pissy about it, but he had dismissed both of your objections. "Hey, Blueberry. Couldn't sleep?" 

He shook his head. "TOO MUCH TRAINING TO ACCOMPLISH. ALPHYS WANTS TO GO ON A RUN IN A FEW HOURS, SO I WANT TO HAVE ALL MY GEAR CLEANED AND LIMBS STRETCHED." He glanced down to Sans. "I GUESS THE LAZY BONES FORGOT ABOUT THE SESSION, HUH?" 

"Um-" 

"NO, OF COURSE NOT." A crimson pupil glared up at the skeleton. Even though he had only just been asleep, his voice sounded perfectly alert. "I HAVE NO GEAR TO CLEAN, OR NEED TO STRETCH MY LIMBS. WE'RE MADE OF BONE, IDIOT." He pressed his face back into your stomach. "I'D RATHER SPEND THAT TIME WITH MY HUMAN." 

For a fraction of a second, you saw a glare cloud Blueberry's features, but it was gone as soon as it came, replaced with his usual smile. "THE HUMAN SHOULD COME WITH US, DON'T YOU THINK?" Your face fell at his words, you knew where this was going. "THAT WAY SHE CAN LEARN MORE ABOUT THIS WORLD." 

"A WORLD WE WON'T BE STAYING IN." 

"FOR ALL YOU KNOW." 

You moaned and fell back against the pillows. "Guys, please shut up. If you don't, I'm gonna go sleep with Papyrus." 

The ensuing silence was like music to your ears.  

* * *

The next morning you stood at the stove flipping pancakes, when the front door burst open. You didn't even have to look to see who it was, the cursing and flood of magic in the house was a heavy hint. "Hey, Sans."

The heavy footfalls came closer, until they were right behind you. A flick of the wrist, and you got the pancake out of the frying pan, before turning to your lover. Red eyes stared you down, the gold pupils morphing into stars when he took you in. You had worn your collar, and leash, your shirt unbuttoned enough to show off your cleavage. A small gift for him, something to help blow off steam. Papyrus had sentry duty in Hotland, and Blueberry was off in Waterfall with Alphys doing something for Undyne. 

"So the puppy know her place."

You hummed, and reached behind you to turn of the burner...

Just to burn your fucking hand. 

You yelped and retracted your hand, the putrid smell of burnt flesh filling the room. You didn't even get the chance to look at it before it was in Sans's gloved hand, his eyes narrowed as he looked your wound over. The skin was puckered, and there was discoloration around the edges, but other than that it was fine. He sighed and brought the hand up to his fangs in a pseudo kiss, sockets closed. "DON'T DO SUCH FRIVOLOUS THINGS. ONLY I CAN HARM YOU IN SUCH A MANNER."

A bright red tongue snaked out from between his teeth, and lapped at the wound. It snaked and curled around your flesh like a snake, then tightened, before loosening and going the opposite direction. You felt your face going warm at the overt display of affection, and your hand reached out, petting his skull. He paused in his coddling, and a grin broke out on his skull. "DOES THE PUPPY STILL WANT ME?"

He snaked his way up your wrist and arm, quiet mewls of acceptance escaping your lips. You brought your body closer to his, a leg sliding up his own. He gave up on your arm all together, and pressed his lips to yours. He tasted like instant ramen and black currants. A strange mixture that got you excited because it was uniquely him. You gasped when he lifted you up, and set your ass on the tile countertop. The cold made your shudder, but Sans' roaming hands was enough to distract you. The gloved appendages trailed down your ass and to your thighs, giving them a tight squeeze. He gave a buck of his hips, and you weren't the least bit surprised to find he already materialized his dick. 

You spread your legs a bit further, and made a low whimper. He growled and bucked into you again, clearly happy with your show of want and submission. He lowered himself down and pulled up your skirt, his eyes narrowing when he saw you with underwear on. "YOU KNOW BETTER, PUPPY. I MUST PICK OUT ALL OF YOUR UNDERGARMENTS, AND THESE," He flicked the elastic band. "ARE NOT TO MY STANDARDS. I WILL NOT TOLERATE SUCH CHEAP AND HIDEOUS THINGS ON MY PUPPY."

The sound of tearing cloth filled the room, and he tossed the underwear into the sink behind you. He then spread your legs further, before you felt a warm appendage teasing your outer lips. You gasped when it dipped inside and gave a firm lap to your clit. Your fingers dug into your palm, resisting the urge to pull him closer to you. A chuckle reverberated against your sensitive body, and he passed his tongue over your clit again. 

You gripped the counter as Sans ate you out. He had a death grip on your thighs, and sweat was beading down your face. A harsh shove of his tongue inside your hole had you throwing your head back, a loud moan echoing through the kitchen. He let his tongue twist around in your tight hole, caressing the top of your walls, before receding back at a snail's pace. Just when you got antsy, he would shove himself back in with a vengeance. 

He retreated completely while you were on the cusp of your orgasm, his face tinted a pale red, and pupils morphed into gold stars. He threaded his fingers at the back of your head, and hauled you upward, bringing you into a bruising kiss. When he pulled away, his fingers caressed your cheek. "I SHOULD TAKE A PICTURE OF YOU LIKE THIS. IT'S PERFECT FOR MY COLLECTION."

You opened your mouth to reply, but faltered when you caught sight of bright blue. Blueberry was at the corner of the door way, the hem of his t-shirt between his teeth, and his hand working a blue dick. He blinked when he noticed your stare, and he straightened up, just to smack his skull against the wall. Sans fingers on your face faltered, and he twisted around, bones materializing in the air with a pop and sizzle. "THE FUCK ARE _YOU_ DOING?"

Blueberry, fiddled with his pants, but his erection was in the way, the engorged member not disappearing. "I-I'M JUST-"

"YOU'RE JUST GOING TO GET DUSTED." The words were a snarl. "YOU'RE ALWAYS STARING AT SOMETHING THAT ISN'T YOURS. WELL GUES WHAT, I'M SICK OF IT." He launched a few of the bones, and you flinched when they were easily knocked aside from pale blue magic. Blueberry's left pupil was missing, leaving a flaming blue on in his right. "SO THE BRAT CAN FIGHT AFTER ALL. DOESN'T MATTER. I'LL KILL YOU AND FUCK HER IN YOUR DUST, MAYBE I'LL EVEN BREED HER."

"YOU REALLY THINK YOU'RE SOME KIND OF HOT SHOT. HOW DO YOU EVEN KNOW IF SHE REALLY LOVES YOU?" Blueberry said, and gestured to you with his free hand. "SHE ACTS SCARED OF YOU ALL THE TIME. MAYBE SHE WANTS TO FEEL CARED FOR?"

 You had to stop this or they would end up killing each other. Then both Papyrus' would hunt you down and kill you. Your teeth sank into your bottom lip as you watched their shouting match. They both loved you because, in theory, you were both of their soul mates. Granted, there was a you in this world too, Blueberry just hadn't met her yet. Sans was ridiculously protective and obsessive over you, and this was something Blueberry wasn't going to be able to walk away from. You had to stop them for good somehow.

This would be so much easier if they weren't-

Your thoughts ground to a halt, and a smile took up your face. You were never allowed to do this without Sans, but you would accept punishment just this once. You spread your legs, and snaked threes fingers down to your pussy, and pressed your thumb against your clit. A loud moan escaped your lips as you pressed down and thrust. Almost immediately all eyes were on you.

Good.

"Master, please." You spread your legs further. "Don't you want to fuck me, or should I ask someone else?"

The now oval pupils narrowed, leaving just the red iris to be visible. A deep snarl rattled his ribcage, and he snatched you off the counter. He shoved your back into Blueberry's ribcage, his dick rubbing against your ass. "YOU WANT SOMEONE ELSE TO FUCK YOU? FINE. I'LL PROVE TO YOU THAT I'M THE ONLY ONE TO MAKE YOU FEEL GOOD."

Blueberry scoffed, but said nothing as his gloved hands cupped your breasts. He pinched the already pert nipples, while Sans gripped your hips thighs and forced your legs to encircle his hips. His own cock had appeared, a bright red with a row of vertical studs on both sides. He lined it up with your pussy, before forcing it in. You moaned and leaned further into Blueberry, your walls stinging from the harsh treatment. Behind you, a cold tongue lapped at your neck, spreading a cold slime along your skin. Every so often you felt teeth sink into your neck, but the pain was quickly soothed the pain. The hands on your breasts squeezed harder, and you knew there was going to be bruises. 

"I'M GONNA FUCK YOU SO GOOD, KITTY."

You felt another cock line up at your entrance, and you shook your head. "I-It's not gonna fit. Please-Ah!"

You had never felt so stretched in your life. The grip on both your tits and thighs tightened, and you let out a choked sob as Blueberry pushed himself inside your pussy. All the while whispering compliments and encouragement. Even Sans had stilled his pace, pressing his teeth to your neck in a pseudo kiss. Your walls flexed and stung as they got used to the new intruder, your breathing heavy. 

You were doing this for a good reason. You were trying to stop these two from dusting each other by accident or on purpose. You could endure a little pain, you've had worse. 

"I'M GOING TO MOVE NOW, KITTY." Blueberry said. "WE CAN STOP IF IT HURTS TOO MUCH."

Sans grunted in agreement as you felt Blueberry pull back a solid two inches,  before sliding back in. When you didn't explode into a flurry of tears, he repeated the movement. At this slow pace you felt full yet...needy. A low moan escaped your lips, causing Sans to growl and buck his hips, adding to your pleasure. It wasn't long before they were both going at a break neck pace, fucking you into oblivion. And that awkward standing position wasn't even the end of it. After you had cum, Sans had dragged you off Blueberry's cock, and fucked you on the kitchen floor, ass in the air, and mouth sucking Blueberry's cock. After awhile you had taken both of their cocks in your pussy again while sitting on the floor. Then Bluberry had taken you while leaning against a wall, while Sans used your tits to jack him off.

By the end of it you were covered in cum and sore. However, both stared down at you expectantly, cocks still out and throbbing. 

"SO," Blueberry said. "WHO DID THE BEST?"

Sans scoffed and knelt down, his cock passing over your slick thighs as he pet your face. "OBVIOUSLY IT WAS ME. I AM HER MASTER, AFTER ALL."

"WHAT?! HOW DO YOU KNOW? SHE DIDN'T EVEN ANSWER."

"Guys."

"THEN MAYBE WE SHOULD DO THIS AGAIN?"

Blueberry nodded. "YOU'RE RIGHT, WE SHOULD DO IT AGAIN SO SHE HAS MORE DATA, RIGHT?"

"Guys?"

"STOP TRYING TO SOUND SMART, IDIOT." He jerked you up, and pressed his fangs to your swollen lips. "NOW STICK YOUR DICK INSIDE OF HER SO WE CAN START."

**Author's Note:**

> That was my first time writing a threesome...So uh...Was it shit? I mean, I have no idea if it was realistic or not. XD I've seen some porn of threesomes before, but we know how accurate porn is. 
> 
> Know what is accurate? My tumblr! http://nihilismpastry.tumblr.com


End file.
